Recently, two separate lines of research were converged by the novel discovery that a protein induced by environmental stress and a protein associated with steroid hormone receptors is, in fact, the same protein. This protein having a molecular weight of approximately 90,000 daltons (90K protein) had been independently characterized as l) a member of a family of 'heat-shock' proteins whose rate of synthesis, levels of mRNA, and steady-state intracellular concentrations are elevated following exposure of eukaryotic cell types to elevated temperature or to treatment with certain cytotoxic agents, and 2) the non-steroid binding component of nontransformed, cytosolic sterioid hormone receptor complexes. This exciting discovery is suggestive of a similar functional role for this common protein which is as yet unknown for either regulatory mechanism. The specific aims of this proposal are focused on characterizing the interaction of environmental stress and steroid hormone function and structure in the simple eukaryotic microbe, Achlya ambisexualis. This aquatic fungus is known to possess a steroid hormone receptor similar to those found in higher organisms and to exhibit changes in gene expression following heat shock. It is proposed to: 1) determine the effect of heat shock on the induction of male sexual differentiation by the fungal sex hormone antheridiol; 2) characterize the effect of heat shock on the biochemical properties of the antheridiol receptor protein; 3) determine the effect of antheridiol exposure on the response to heat shock and 4) develop methods to isolate and purify the heat shock proteins in Achlya for production of monoclonal antibodies as useful tools for future studies on the physiological role of these proteins. Results of these studies will provide new information on the relationship between environmental stress and the mechanism of action of sterioid hormones. The Achlya system is ideally suited for the proposed studies because its environment is easily manipulated; the steroid-induced biological response is a rapid, directly observable morphological change, the steroid receptor level within the cell can be regulated by alterations in the nutrient supply and we have produced a monoclonal antibody to the 90K heat-shock protein found in Achlya.